Turbochargers increase the volumetric efficiency and power output performance of an internal combustion engine. Turbochargers function by increasing the pressure of the air supplied to the engine. Turbochargers are popular optional equipment on high performance vehicles because they provide faster response upon acceleration and greater horsepower.
Briefly, a turbocharger is an air pump which provides a compressed charge of air to the combustion chamber of the engine. In current automotive turbochargers, the turbocharger is a turbine that supplies compressed air to the throttle body unit or intake manifold, of an internal combustion engine. The compressor is connected by a shaft to an exhaust gas turbine. Exhaust gas exiting the engine rapidly rotates the exhaust gas turbine. The exhaust gas turbine turns the shaft and rotates the air compressor.
The boost pressure achieved by the turbocharger is controlled to protect the engine. Boost pressure is controlled by a wastegate that permits exhaust gases to bypass the exhaust gas turbine. The wastegate is operated by an actuator which opens and closes the wastegate. The actuator is operated by vacuum or pressurized fluid. The actuator is controlled by a pulse train generated by the engine control module, or on-board computer.
The engine control module pulse train is received by a solenoid-controlled vacuum valve. The pulse train energizes and de-energizes the solenoid sequentially causing the actuator to open and close the wastegate. The wastegate opens to permit exhaust gases to byspass the exhaust gas turbine. Under normal driving conditions, the control solenoid is energized 100% of the tiem, closing off the manifold to the wastegate actuator. When the wastegate is closed, boost pressure increases rapidly. The manifold air pressure sensor monitors the increase in pressure and, if appropriate, signals the engine control module to pulse the wastegate control valve on and off. This pulsing on and off prevents an over boost condition on rapid acceleration.
With original equipment turbochargers, boost pressure increases to about 9 psi. Then the engine control module functions to inhibit further increase in boost pressure. This limited boost pressure is well within the limits of the engine's capabilities even at higher engine speeds. At lower engine speeds the limitation on maximum boost pressure is unnecessary because engine stress is not high at engine speeds of 2000 to 3500 rpms.